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Endocrinol Diabetes Nutr. 2017 Oct;64(8):417-423. doi: 10.1016/j.endinu.2017.06.002. Epub 2017 Jul 29.

Definition of reference ranges for free T4, TSH, and thyroglobulin levels in healthy subjects of the Jaén Health District.

[Article in English, Spanish]

Author information

UGG de Urgencias, Complejo Hospitalario de Jaén, Jaén, España.
UGC Endocrinología y Nutrición, Complejo Hospitalario de Jaén, Jaén, España. Electronic address:
UGC de Aparato Digestivo, Hospital Universitario Virgen de la Victoria/Instituto de Investigación Biomédica de Málaga, Málaga, España.
Distrito Sanitario de Jaén, España.
UGC Endocrinología y Nutrición, Complejo Hospitalario de Jaén, Jaén, España.
UGC de análisis Clínicos, Complejo Hospitalario de Jaén, Jaén, España.



The treatment guidelines for thyroid dysfunction recommend defining reference ranges for thyroid hormones in each area through assessment of local population data considering the iodine nutritional status. The aim of this study was to define the reference ranges of free thyroxine (FT4), TSH, and thyroglobulin levels in a general population from Jaen, an area of southern Spain with an adequate iodine nutritional status, and whether they were associated with urinary iodine levels.


A cross-sectional study was conducted in 1,003 subjects of the general population of the Jaen Health District. Levels of urinary iodine, FT4, TSH, thyroglobulin, and thyroid peroxidase (TPO) antibodies were measured according to age and sex.


Median and mean urinary iodine levels were 110.59μg/L and 130.11μg/L respectively. Median TSH level was 1.83μIU/mL (p2.5=0.56μIU/mL, p97.5=4.66μIU/mL). Median FT4 level was 0.84ng/dL (p2.5=0.62ng/dL, p97.5=1.18ng/dL). TPO antibodies were detected in 5.7% of subjects. There was no correlation between urinary iodine levels and FT4, TSH or TPO antibodies. Subjects with positive TPO antibodies had higher TSH levels (3.34μIU/L versus 2.14μIU/mL, P=.001; odds ratio=2.42).


Urinary iodine levels in Jaen are optimal according to World Health Organization standards. Reference ranges of FT4, TSH, and thyroglobulin do not differ from those reported in the literature and are no associated to urinary iodine levels. The prevalence of positive TPO antibodies was similar to that reported in other Spanish areas.


Hormonas tiroideas; Iodine intake; Nutrición yódica; Thyroid hormones; Urinary iodine levels; Yoduria

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